WO2025067869A1 - Assembly of a laminated glazing having structural folds made of glass pierced with holes for receiving screws rigidly connected to an aircraft structure, the contact of the screws transmitting membrane forces to the structural folds - Google Patents

Abstract

The invention relates to a system or an assembly comprising a laminated glazing, consisting of at least one first outer glass sheet (1) set back with respect to at least two structural glass sheets (3, 5), bonded pairwise by an adhesive interlayer (2, 4), wherein the peripheral portion of the structural glass sheets (3, 5) overhanging the first glass sheet (1) comprises through-holes, in which screw-nut assemblies (11) are screwed in order to rigidly connect the structural glass sheets (3, 5) to a mounting structure (17), each through-hole is cylindrical and a cylindrical interface system (15) is positioned between the through-hole and the screw (11), or each through-hole has, in each of the structural glass sheets (3, 5), a conical or biconical geometry, for the insertion of studs (21, 22) of corresponding conical or biconical geometry, with a conical or biconical clamping interlayer (23) positioned therebetween; a method for producing this system.

Description

Description

Title of the invention:

ASSEMBLY OF A LAMINATED GLAZING WITH STRUCTURAL GLASS PLY DRILLED WITH HOLES TO ACCOMMODATE SCREWS ATTACHED TO AN AIRCRAFT STRUCTURE, THE CONTACT OF THE SCREWS TRANSMITTING MEMBRANE FORCES TO THE STRUCTURAL PLY

[1]The invention relates to aeronautical cockpit glazing, which is a laminated glazing usually made up of two or three layers of organic or mineral glass or a mixture of the two. The glazing provides the crew with sufficient vision (in particular by implementing anti-icing and/or anti-fogging heating systems) at all times to enable piloting operations in complete safety.

[2]Membrane forces, i.e. traction in the plane of the aircraft structure (fuseboard) are the consequence of the pressurization of the interior volume of the aircraft.

[3]From a structural point of view, aircraft cockpit glazing can be divided into two categories:

- glazing not working in membrane: they do not transmit or transmit very little of the membrane forces associated with aircraft pressurization;

- working glazing which transmits membrane forces. The structure-glazing connection system is therefore capable of transmitting membrane forces typically of 50 to 300N/mm.

[4] The folds transmitting the membrane forces can be either made of organic glass (PMMA, PC) or mineral. In the latter case, the known technique consists of adding wedges (or heels) made of fiberglass or titanium composite materials which are pierced and mechanically bonded to the structural glasses by gluing thin inserts also made of fiberglass or titanium composites.

[5] Glass-based aeronautical glazing capable of withstanding membrane forces therefore uses composite or, exceptionally, titanium heels which are drilled to bolt the glazing to the aircraft structure. The glued thin inserts transmit the forces from the heels to the glass folds. The manufacture of the heel/insert system is industrially complex because it requires strict manufacturing tolerances and complex processes. Furthermore, the heels and inserts on the periphery of the glazing are not transparent and therefore impose significant non-functional areas.

[6]Among the optical defects of glazing, inclusions of particles and dust are among the critical defects. The use of composite materials (heels, inserts) before the dust-free assembly phases of laminated glazing can generate optical defects through dust inclusion.

[7]It appears critical to ensure good alignment of the heels (or shims) with respect to the glass sheets that they extend and good flatness of the composite inserts in order to ensure control of the stress paths and maintain the optimal mechanical performance of the assembly. Indeed, due to their low thickness, the composite inserts which drain all the membrane forces must have good flatness to avoid stress concentrations. [8]The management of shape conformities between the glass and the composite shims (which for reasons of tooling costs and material consumption are advantageously produced in several pieces) poses a problem, as does the correct positioning of the composite folds of the insert.

[9] Structural bonding is a special process which can be sensitive to glass pollution, raw material drift and implementation defects.

[10]In a composite attachment glazing, a certain number of attachment failures (detachment, composite insert breakage, hole breakage) may remain invisible in service and/or during inspection. This results in an overload of the aircraft structure leading either to an acceleration of its fatigue or the need for oversizing to prevent this risk.

[11]The mechanical stress on glazing is cyclical, where a cycle corresponds to the aircraft being pressurized on each flight. However, composites and bonding can be sensitive to cyclic fatigue, temperature and humidity. In particular, it is particularly difficult to protect the insert and its bonding on the internal face of the internal glass, which is particularly exposed to condensation humidity (unheated area of the glazing).

[12]The inventors have imagined solving these problems by designing a working glazing in which the transmission of membrane forces to the structural glass folds is achieved by contact between screws mechanically secured to the aircraft structure and the structural glass folds at the level of holes drilled directly in the latter. The problems described above have thus been solved by the invention, which relates to a system or assembly comprising laminated glazing intended to close a volume subjected to repeated pressurization over long periods, essentially consisting of at least a first mineral glass sheet and at least two structural mineral glass sheets bonded two by two by an interlayer adhesive layer, the main free surface of the first glass sheet being intended to be in contact with the external atmosphere, the first glass sheet being set back relative to the structural glass sheets, characterized in that the peripheral part of the structural glass sheets projecting from the first glass sheet comprises through holes, in that the assembly comprises screw nuts capable of being screwed through each of said through holes, to secure the structural glass sheets to a mounting structure, in that each of said through holes is cylindrical and the assembly comprises a cylindrical interface system which is interposed between said through hole and the screw, or each of said through holes present in each of the structural glass sheets, a conical or biconical geometry, and the assembly comprises studs of corresponding conical or biconical geometry, intended to be inserted into the part of each through hole in each structural glass sheet, and the assembly comprises a conical or biconical clamping spacer to be interposed between each stud and the part of said through hole belonging to each of the corresponding structural glass sheets.

[13]The screws are made of hard metallic material such as titanium.

[14]When the through holes are cylindrical, the transmission is done by a pin loaded contact. The screw-glass connection is made by interposing the cylindrical interface system in a relatively soft material, single-component or multi-material: one can use a flexible metal such as aluminum or a polymer material such as polyoxymethylene (POM), poly(methyl methacrylate) (PMMA), polycarbonate (PC), and/or rubber-type elastomer. This interface system performs two functions:

- it avoids direct contact between the hard screw and the glass to avoid contact breaks, and - it allows for attachment flexibility that accommodates manufacturing tolerances.

[15]When the through holes in each of the structural glass sheets have a conical or biconical geometry, the transmission of forces is done by bolting, that is to say by preventing slippage by tightening the assemblies. The bi- or tetra-conical assembly system binds the two structural glass layers together. A tightening spacer is positioned between the conical or biconical surface of the holes and the conical or biconical surface of the studs, in each structural glass sheet.

[16]Drilling in glass according to the invention reduces the optically unnecessary non-transparent fractions of the glazing by eliminating the heel wedges and thin composite inserts. This elimination virtually eliminates the risks of inclusion of particles and dust. Direct drilling in the glass widens the shape tolerances of the glasses at the periphery. It can be very automatable and destructive verifications can be easily carried out to verify the capability of the processes.

[17]Furthermore, in accordance with the invention, the structural failures correspond to glass breakages at the hole which cause the complete breakage of the glass fold. This failure mode is immediately visible to the pilot and makes it possible to make the aircraft safe with regard to structural fatigue. Glass is a material that is not very sensitive to cyclic fatigue mechanisms (pressurizing the aircraft during each flight), not very sensitive to temperature and humidity unlike composites and to bonding, particularly critical on the internal face of the internal glass exposed to condensation humidity (unheated area of the glazing).

[18] In a first variant, the system or assembly comprises an external retainer and a belt intended to be secured to the external and internal peripheral surfaces of the block of structural glass sheets, extending beyond the first glass sheet, by means of the screw nuts, the external retainer is also intended to be fixed to the mounting structure, and the assembly comprises two layers of mastic interposed between the block of structural glass sheets and the external retainer on the one hand, the belt on the other hand.

[19]Preferably, the cylindrical interface system has a length equal to the original distance to be maintained between the external retainer and the belt; it thus makes it possible to avoid crushing the interlayer adhesive layer bonding the structural glass sheets together.

[20]In a second variant, the system or assembly comprises an outer cover, a layer of mastic and a thickness shim, the outer cover is intended to be secured to the outer peripheral surface of the block of structural glass sheets, overhanging the first sheet of glass, by means of the screws and nuts, with the interposition of the layer of mastic on the one hand, and the mounting structure is intended to be secured to the inner peripheral surface of the block of structural glass sheets, overhanging the first sheet of glass, by means of the screws and nuts, with the interposition of the thickness shim on the other hand. The outer cover is flush with the first sheet of glass, ensuring the aerodynamic continuity of the latter with the mounting structure (aircraft structure, fuselage).

[21]Preferably, the system or assembly comprises, in each interlayer adhesive layer bonding the structural glass sheets two by two, a peripheral reinforcing insert made of metallic or composite material or fabric completely surrounding the screw area, cylindrical interface systems, extensions of the studs in the interlayer adhesive layer as appropriate, which allows the transmission of membrane forces between the mounting structure and the interlayer adhesive layer in the event of rupture of all the structural glass sheets. This peripheral insert is designated by the English term “fail safe” insert, in that it allows the adhesive layer interlayer to assume the function of mechanical resistance of the laminate when all the structural glasses break.

[22]Preferably, the system or assembly comprises, in each interlayer adhesive layer bonding the structural glass sheets two by two, a clamping washer completely surrounding the screw area, cylindrical interface systems, extensions of the studs in the interlayer adhesive layer as appropriate, the clamping washer having the same thickness as the interlayer adhesive layer and being made of a stiffer material than the latter, so that the tightening of the screws, studs, does not compress the interlayer adhesive layer. This clamping washer thus performs the same function as the cylindrical interface system made of aluminum or equivalent, when it has in particular a length equal to the original distance to be maintained between the external retainer and the belt. The clamping washer is significantly stiffer in compression than the interlayer adhesive layer.

[23] Preferably, the glass sheets are made of mineral glass such as soda-lime silico, aluminosilicate, borosilicate or the like, in particular thermally toughened or preferably chemically reinforced, the first glass sheet has a thickness of between 2 and 5 mm, and the structural glass sheets have a thickness of between 2 and 10 mm, and the face of the first glass sheet facing the structural glass sheets carries a de-icing heating coating of the indium tin oxide (ITO) type (front windshield), or a structural glass sheet (preferably the penultimate one starting from the first glass sheet) carries an anti-fog heating coating of an equivalent nature (side window).

[24]Preferably, the interlayer adhesive layers are made of polyvinyl butyral (PVB), thermoplastic polyurethane (TPU), ethylene-vinyl acetate copolymer (EVA) or ionomer resin, the interlayer adhesive layer bonding the first glass sheet to the structural glass sheets has a thickness of between 2 and 8 mm and each interlayer adhesive layer bonding the structural glass sheets together two by two has a thickness of between 1 and 4 mm.

[25]Another object of the invention consists of a method for producing a system or assembly described above, characterized in that it comprises

- cutting of flat glass primitives,

- high temperature shaping of glass sheets or folds,

- drilling of glass sheets,

- chemical strengthening of glass sheets,

- the assembly of glass sheets, interlayer adhesive layers, cylindrical interface systems or dowels and clamping spacers, and if used, peripheral inserts and clamping washers,

- autoclaving, in which the flow of the interlayer adhesive layers ensures the sealing on the outside of the cylindrical or stud interface systems. The drilling of the glass sheets preferably includes a rounded finish of the edges. The Chemical strengthening allows strengthening of the interior of the holes, whereas it is complex to quickly cool the interior of the holes during thermal quenching.

[26]Preferably, the method then comprises

- bolting the external retainer, from the belt to the glazing using the screws and nuts,

- application of sealing mastic and compensation of shape tolerance.

[27]Preferably, the method comprises the addition after lamination, depending on the configuration, of the shim which can then undergo final machining to ensure good shape control.

[28]Preferably, the method then comprises bonding the outer cover to the free peripheral surface of the structural glass sheet extending beyond the first glass sheet, bonding such as by the layer of mastic.

[29]Preferably, the drilling of the glass sheets is mechanical such as by diamond cutter, or by laser.

[30]The invention will be better understood in light of the following description of the appended figures in which

[Fig. 1] is a schematic sectional view of a state-of-the-art laminated glazing unit,

[Fig. 2] and [Fig. 3] are two schematic sectional representations of two variants of the first main embodiment of the working glazing of the invention, and

[Fig. 4] is a schematic sectional representation of the second main embodiment of the working glazing of the invention.

[31]All the glazings shown comprise three sheets of chemically reinforced aluminosilicate glass: a first sheet 1 3 mm thick, a second and a third structural sheet 3, 5 8 mm thick. They are bonded two by two by means of two layers of PVB or TPU: a layer 2 2 to 8 mm thick between the first sheet 1 and the second structural sheet 3, and a layer 4 1 to 4 mm thick between the two structural glass sheets 3, 5.

[32]With reference to Figure 1, the membrane forces are transmitted to the structural glass sheets 3, 5 by thin composite inserts 7 glued to the glasses 3, 5 by the glue 8, on the one hand, bolted with peripheral wedges or heels 6 made of composite, between an external retainer 12 and a belt 13. The structural glass sheets 3, 5 are thus secured to the aircraft structure not shown, in that the external retainer 12 is also intended to be fixed to the aircraft structure. The plugging, sealing and shape adjustments are carried out by injecting mastic 14 between the external retainer 12 and the insert 7 exterior, and between the belt 13 and the interior insert 7. The sealant consists of polysulfide, in particular known under the references PR (precisely PR 1440 M Class B) consisting of a two-part product based on polysulfide liquid rubber and a manganese-based accelerator. These combined precursors polymerize at room temperature, to obtain a firm and flexible sealing sealant with excellent adhesion to Al, Ti, steel in particular.

[33]With reference to Figure 2, the structural glasses 3, 5 comprise cylindrical holes aligned with each other, in the peripheral part of each structural glass sheet 3, 5 overhanging the first glass sheet 1. A cylindrical interface system 15 made of aluminum is inserted into the holes of the structural glass sheets 3, 5, interposed between the titanium screw 11 and the edges of the holes in the structural glass sheets 3, 5. The cylindrical interface system 15 is of length equal to the distance between the external retainer 12 and the belt 13, so as to sustainably maintain the value of this distance. The titanium screw also passes through a hole drilled in a peripheral insert 16 made of composite material, placed in the adhesive layer 4 so as to allow it to carry out the membrane forces to keep the glazing fixed to the aircraft structure, even in the event of breakage of all the glass sheets 3, 5 and obviously 1.

[34]Filling the gaps with 14 polysulfide PR mastic makes it possible to ideally achieve decoupling between the shape of the glasses and that of the aircraft structure. This requires that the shape of the external retainer 12 be finely controlled.

[35]The glazing can be fixed to the external retainer 12 by the nut screws 11 in the factory by the glazing manufacturer. The mastic 14 is also factory-applied: it tolerates long crosslinking times and is compatible with complex centering strategies.

[36]In Figure 3, the transmission of membrane force between the aircraft structure 17 and the glazing is done by the inner surface of the glazing. The glazing is fixed by means of the screws-nuts 11 to the aircraft structure 17 by its inner peripheral surface (free peripheral surface of the second structural glass sheet 5), overhanging the first glass sheet 1. A shim 19 is interposed between the second structural glass sheet 5 and the aircraft structure 17, so as to be able to be machined to adjust the position of the laminated glazing relative to the aircraft structure 17. A clamping washer 20 is inserted into the interlayer adhesive layer 4, it is made of a material stiffer in compression than that of the latter 4, for example an epoxy-glass composite, so as to ensure the same function as the cylindrical interface system 15 in Figure 2. [37]The glazing is here fixed by means of the screws and nuts 11 directly on the aircraft. The use of overly complex mastics directly on the aircraft is prohibited. This is why, as specified above, it is preferred here to place a dry shim between the aircraft structure 17, acting as an internal retainer, and the structural glass 5. This shim must allow the shape tolerances of the glazing to be accommodated, either by being machinable after assembly to the glass to conform to the aircraft shape, or by gluing it with a sufficient thickness of glue to accommodate the variations in the shape of the glass (typically 1 mm).

Using the screws and nuts 11, an outer cover 18 is screwed onto the free outer surface of the outer structural glass sheet 3, extending beyond the glass sheet 1, with the interposition of polysulfide PR mastic 14. The outer cover 18 must be in aerodynamic continuity with the aircraft, which requires allowing room for maneuver. In this case, it is possible to consider gluing the outer cover 18 to the glazing in the factory (which allows the use of mastic 14). Another option is to use a dry shim as described above. It is also possible to inject a silicone seal by overmolding, as is more conventionally done on aeronautical glazing.

[38]Tests were carried out on a “pin loaded” configuration similar to that of Figures 2 and 3 on a 6mm thick, chemically reinforced perforated glass ply. 12 to 13kN/8mm diameter hole were transmitted for symmetrical loading (double strap) with a 5mm diameter steel screw with an aluminium tube with an internal and external diameter of 8 and 6 mm respectively interposed between the glass hole and the loading screw.

[39]For a laminated configuration of two glasses as above loaded eccentrically, breaking loads of 8 to 10 kN/hole were obtained.

[40] In Figure 4, the peripheral part of each structural glass sheet 3, 5 extending beyond the first glass sheet 1 is pierced with conical holes to accommodate a stud 21, 22 of corresponding shape. The conical hole of the outer structural glass sheet 3 has a diameter decreasing from the outside to the inside, from top to bottom in Figure 4, while the conical hole of the inner structural glass sheet 5 has an increasing diameter from the outside to the inside. Other possible configurations are the two conical holes together of equally increasing diameters, respectively decreasing from the outside to the inside, or the two biconical shaped holes, each of decreasing diameters, then increasing from the outside to the inside. The cylindrical extension of the inner stud 22 in the intermediate adhesive layer 4 can be inserted by screwing into the hollow cylindrical extension of the outer stud 21 in the intermediate adhesive layer 4. A conical clamping spacer 23 is interposed between each stud 21, 22 and the conical hole of each structural glass sheet (3, 5).

[41]In a 6 mm thick sheet of glass, a biconical through hole (45° angle) was made, with decreasing diameters from 13 to 8 mm along half the thickness of the glass sheet (i.e. 3 mm), then increasing from 8 to 13 mm along the other half of this thickness, in each of the two directions perpendicular to the main surfaces of the glazing. A stud of corresponding biconical geometry is inserted into the through hole, with the interposition of a biconical tightening spacer. The two conical parts of the stud are assembled by screwing using a 6 mm diameter threaded rod integral and concentric with a conical half-stud, and a corresponding threaded hole in the second threaded half-stud. Maximum loads of 16 kN are measured.

Claims

Claims 1. Assembly comprising laminated glazing intended to close a volume subjected to repeated pressurization over long periods, essentially consisting of at least one first mineral glass sheet (1) and at least two structural mineral glass sheets (3, 5) bonded two by two by an interlayer adhesive layer (2, 4), the main free surface of the first glass sheet (1) being intended to be in contact with the external atmosphere, the first glass sheet (1) being set back relative to the structural glass sheets (3, 5), characterized in that the peripheral part of the structural glass sheets (3, 5) projecting from the first glass sheet (1) comprises through holes, in that the assembly comprises nut screws (11) capable of being screwed through each of said through holes, to secure the structural glass sheets (3, 5) to a mounting structure (17), in that each of said through holes is cylindrical and the assembly comprises a cylindrical interface system (15) which is interposed between said through hole and the screw (11), or each of said through holes has in each of the structural glass sheets (3, 5), a conical or biconical geometry, and the assembly comprises studs (21, 22) of corresponding conical or biconical geometry, intended to be inserted into the part of each through hole in each structural glass sheet (3, 5), and the assembly comprises a conical or biconical clamping insert (23) to be interposed between each stud (21, 22) and the part of said through hole belonging to each of the corresponding structural glass sheets (3, 5). 2. Assembly according to claim 1, characterized in that it comprises an external retainer (12) and a belt (13) intended to be secured to the external and internal peripheral surfaces of the block of structural glass sheets (3, 5), overhanging the first glass sheet (1), by means of the screw nuts (11), in that the external retainer (12) is also intended to be fixed to the mounting structure (17), and in that the assembly comprises two layers of mastic (14) interposed between the block of structural glass sheets (3, 5) and the external retainer (12) on the one hand, the belt (13) on the other hand. 3. Assembly according to claim 2, characterized in that the cylindrical interface system (15) has a length equal to the original distance to be maintained between the external retainer (12) and the belt (13). 4. Assembly according to claim 1, characterized in that it comprises an outer cover (18), a layer of mastic (14) and a shim (19), in that the outer cover (18) is intended to be secured to the outer peripheral surface of the block of structural glass sheets (3, 5), overhanging the first glass sheet (1), by means of the screws and nuts (11), with the interposition of the layer of mastic (14) on the one hand, and in that the mounting structure (17) is intended to be secured to the inner peripheral surface of the block of structural glass sheets (3, 5), overhanging the first glass sheet (1), by means of the screws and nuts (11), with the interposition of the shim (19) on the other hand. 5. Assembly according to one of the preceding claims, characterized in that it comprises, in each intermediate adhesive layer (4) bonding the structural glass sheets (3, 5) two by two, a peripheral reinforcing insert (16) made of metallic or composite material or fabric completely surrounding the area of the screws (11), cylindrical interface systems (15), extensions of the studs (21, 22) in the intermediate adhesive layer (4) as appropriate, which allows the transmission of membrane forces between the mounting structure (17) and the intermediate adhesive layer (4) in the event of rupture of all the structural glass sheets (3, 5). 6. Assembly according to one of the preceding claims, characterized in that it comprises, in each intermediate adhesive layer (4) bonding the structural glass sheets (3, 5) two by two, a clamping washer (20) completely surrounding the area of the screws (11), cylindrical interface systems (15), extensions of the studs (21, 22) in the intermediate adhesive layer (4) as appropriate, the clamping washer (20) having the same thickness as the intermediate adhesive layer (4) and being made of a stiffer material than the latter (4), so that the tightening of the screws (11), studs (21, 22), does not compress the intermediate adhesive layer (4). 7. Assembly according to one of the preceding claims, characterized in that the glass sheets (1, 3, 5) are made of mineral glass such as soda-lime-silica, aluminosilicate, borosilicate or the like, in particular thermally toughened. or preferably chemically reinforced, in that the first glass sheet (1) has a thickness of between 2 and 5 mm, and the structural glass sheets (3, 5) have a thickness of between 2 and 10 mm, and in that the face of the first glass sheet (1) facing the structural glass sheets (3, 5) carries a de-icing heating coating of the indium tin oxide (ITO) type (front windshield), or a structural glass sheet (3, 5) (preferably the penultimate (3) starting from the first glass sheet (1)) carries an anti-fog heating coating of an equivalent nature (side window). 8. Assembly according to one of the preceding claims, characterized in that the intermediate adhesive layers (2, 4) are made of polyvinyl butyral (PVB), thermoplastic polyurethane (TPU), ethylene-vinyl acetate copolymer (EVA) or ionomer resin, in that the intermediate adhesive layer (2) bonding the first glass sheet (1) to the structural glass sheets (3, 5) has a thickness of between 2 and 8 mm and each intermediate adhesive layer (4) bonding the structural glass sheets (3, 5) together two by two has a thickness of between 1 and 4 mm. 9. Method for producing an assembly according to one of the preceding claims, characterized in that it comprises - cutting of flat glass primitives, - high temperature shaping of glass sheets or folds (1, 3, 5), - drilling of glass sheets (1, 3, 5), - chemical strengthening of glass sheets (1, 3, 5), - the assembly of the glass sheets (1, 3, 5), the intermediate adhesive layers (2, 4), cylindrical interface systems (15) or studs (21, 22) and clamping spacers (23), and if used, peripheral inserts (16) and clamping washers (20), - autoclaving, in which the flow of the intermediate adhesive layers (2, 4) ensures sealing on the outside of the cylindrical interface systems (15) or studs (21, 22). 10. Method according to claim 9, characterized in that it then comprises - bolting the external retainer (12), the belt (13) to the glazing (1, 2, 3, 4, 5) by means of the screws and nuts (11), - application of the sealing mastic (14) and compensation of shape tolerance. 11. Method according to claim 9, characterized in that it comprises the addition after lamination, according to the configuration, of the thickness shim (19) which can then undergo final machining to ensure good shape control. 12. Method according to claim 9, characterized in that it then comprises bonding the outer cover (18) to the free peripheral surface of the structural glass sheet (3) extending beyond the first glass sheet (1), bonding such as by the layer of mastic (14). 13. Method according to claim 9, characterized in that the drilling of the glass sheets (1, 3, 5) is mechanical such as by diamond cutter, or by laser.